Plural vehicle brake system

ABSTRACT

There is disclosed a shoe drum brake and a braking system utilizing such a brake. The brake has a pair of brake shoes, with a hydraulic expander unit arranged between one pair of adjacent ends of said shoes and a fixed anchorage arranged between the other pair of adjacent ends. The expander unit has two oppositely directed shoe displacing pistons having different cross-sectional areas, which are slidably arranged in corresponding cylinders in the unit so as to assist in positioning the center of pressure of the lining, within the region of the center of area of each shoes&#39;&#39; lining. A shoe drum brake as disclosed, is attached to each wheel of the vehicle, and the leading shoes at the front wheels of the vehicle together with the trailing shoes at the rear wheels are interconnected, and actuable by means for directing pressure fluid from a source of such fluid. The remaining brake shoes are likewise interconnected and arranged for simultaneous actuation with said first mentioned shoes.

United States Patent [72] Inventor Arthur Goddard Solihull, England [21]Appl. No. 820,383 [22] Filed Apr. 30, 1969 [45] Patented Oct. 5, 1971[73] Assignee Girling Limited Birmingham, England [32] Priority May 11,1968 [33] Great Britain [31] 22,448/68 [54] PLURAL VEHICLE BRAKE SYSTEM2 Claims, 2 Drawing Figs.

[52] US. Cl 188/345, 188/327 [51] Int. Cl B60t 11/20 [50] Field ofSearch..188/l52.02, 152.81, 152.82, 327, 345, 78

[56] References Cited UNITED STATES PATENTS 1,630,178 5/1927 Harrington188/152 (.02) 1,943,886 1/1934 Carroll ..l88/152 (.82) X FOREIGN PATENTS877,742 9/1942 France 188/152 (.02) 1,146,888 5/1957 France 188/152(.02)

Primary Examiner-George E. A. Halvosa AttorneyScrivener, Parker,Scrivener and Clarke ABSTRACT: There is disclosed a shoe drum brake anda braking system utilizing such a brake. The brake has a pair of brakeshoes, with a hydraulic expander unit arranged between one pair ofadjacent ends of said shoes and a fixed anchorage arranged between theother pair of adjacent ends. The expander unit has two oppositelydirected shoe displacing pistons having different cross-sectional areas,which are slidably arranged in corresponding cylinders in the unit so asto assist in positioning the center of pressure of the lining, withinthe region of the center of area of each shoes lining. A shoe drum brakeas disclosed, is attached to each wheel of the vehicle, and the leadingshoes at the front wheels of the vehicle together with the trailingshoes at the rear wheels are interconnected, and actuable by means fordirecting pressure fluid from-a source of such fluid. The remainingbrake shoes are likewise interconnected and arranged for simultaneousactuation with said first mentioned shoes.

PATENTED mm 5 Ian I 3,610,378

sum 1 0F 2 PLURAL VEHICLE BRAKE SYSTEM The present invention concernsvehicle hydraulic brakes and relates more particularly to shoe drumbrakes of the type including at least one leading and one trailing shoe.

Modern vehicle practice increasingly requires a vehicle to be providedwith a braking system having a dual operating facility, so that,should'one part or aspect of the system fail in use, the remaining partof the system is still available to operate some or all of the brakes.

According to the present invention, a vehicle braking system comprisesfor each vehicle wheel, a shoe drum brake including at least one leadingshoe and trailing shoe combination, a source of pressure fluid, meansfor directing fluid pressure from said source to actuate the leadingshoes at the vehicle front wheels together with the trailing shoes atthe rear wheels and independent means for directing fluid pressuresimultaneously to actuate the remaining shoes.

By virtue of the braking system provided by the invention, regardless ofthe direction of motion of the vehicle, when one part of the system hasfailed, the vehicle retardation is improved by the fact that one set ofwheel brakes i.e. either those at the front or those at the rear alwayshas its leading shoe applied. This is especially useful in a drum brakewhere no attempt has been made to obtain equal performance from both theleading shoesvand the trailing shoes, for example by arranging for thepressure fluid to apply difierential actuating forces to the differentshoes.

The braking system proposed by the invention is in fact mostconveniently used together with shoe drum brakes in which the shoes aresubjected to differential operating forces and according to anotherfeature of the present invention, there is provided a shoe drum brakecomprising a pair of arcu ate brake shoes each respectively having ashoe lining, with a hydraulically actuated expander unit arrangedbetween one pair of adjacent ends of said shoes and a fixed anchorage orabutment arranged between the other pair of adjacent ends and in whichthe expander unit includes oppositely directed shoe displacing pistonshaving different cross-sectional areas, each piston being received in acylinder of said unit which is inclined to assist in positioning thecenter of pressure of the lining within the region of the center of thearea of the shoe lining. Conveniently, in a brake of this character, thepistons may be arranged for hydraulic actuation independently of oneanother.

According to yet another aspect of the invention, a vehicle brake asdefined in the preceding paragraph hereof may be modified by arrangingthe pistons to be axially aligned with one another rather than in theinclined attitude described.

The present invention will now be further described, by way of example,with reference to the accompanying drawings in which:

FIG. 1 is a radial section of a shoe drum brake, and

FIG. 2 is a diagrammatic illustration of a brake actuating hydraulicsystem embodying the invention.

In the brake shown in FIG. 1, a hydraulic actuator or expander unitgenerally designated is secured to a brake backplate 12 between one pairof adjacent ends of a pair of arcuate brake shoes 14 and 16 displaceableon the backplate, the other ends of the brake shoes being located on afixed anchorage or abutment 18 also secured to the backplate. Shoereturn springs 20 normally retain a running clearance between the shoesand the brake drum (not shown). In FIG. 1, the direction of drumrotation for forward motion is anticlockwise, so that the left handbrake shoe l4 acts as a leading shoe and receives servo assistance fromthe rotation of the drum.

In order to obtain equal work from each shoe and therefore equal life ofthe two linings, the leading shoe 14 is operated with less force fromthe expander unit 10 than the trailing shoe 16. For this purpose, theexpander unit includes a leading shoe actuating piston 22 which is ofless cross-sectional area than the trailing shoe actuating piston 24.The hydraulic cylinders 26 and 28 respectively containing the pistonsare provided with individual hydraulic connections (not shown) toseparate hydraulic pressure generating sources which may either bestatic hydraulic systems controlled by directly or indirectly mastercylinder means or which may alternatively be full flow hydraulic systemsincluding a pump, a reservoir, a hydraulic accumulator if required andfluid flow control valve means preset to deliver selected pistonoperating pressures to the cylinders. It will be noted that thecylinders 26 and 28 are inclined to, assist in positioning the center ofpressure within the"region of the center of area of the shoe linings.

Automatic adjusting means of any convenient type and generallydesignated by the reference numeral 30 in FIG. I is provided for each ofthe brake shoes 14 and 16 adjacent their actuated ends to maintain asubstantially constant running clearance between the shoes and the drumirrespective of condition of wear of the shoe lining. In this way, thequantity of fluid delivered to the cylinders during brake actuation isminimized. v

The brake illustrated in FIG. I is conveniently employed in thehydraulic braking system shown in FIG. 2. FIG. 2 shows a so-calledhorizontally split hydraulic system whereby, irrespective of which ofthe two hydraulic lines should fail, the other line is still capable ofapplying braking effort to all four vehicle wheels. In the illustratedsystem the brake actuating pistons 22 and 24 will'be observed to beconnected in two completely independent hydraulic circuits respectivelydesignated 32 and 34, the circuit 32 being shown in full lines and thecircuit 34 in dash lines. The hydraulic circuit 32 is connected to thetwo pistons 22 associated with the leading brake shoes at the two frontwheels 36 of the vehicle and to the two pistons 24 of the trailing shoesat the rear wheels 38 of the vehicle. The independent hydraulic system34 is con nected in a complementary manner to the two pistons 24 of thetrailing shoes of the front wheels 36 and to the two pistons 22 of theleading shoes of the rear wheels 38. FIG. 2 illustrates hydraulic mastercylinders 40 and 42 respectively operated by pneumatic motors 44 and 46as being provided to pressurize the hydraulic systems 32 and 34 forbrake actuation. It will be appreciated, however, that in place of theillustrated static hydraulic system, the pistons could alternatively beoperated by full flow or dynamic hydraulic systems wherein the operatingpressures are predetermined by preset control valves in turn arrangedfor operation responsive to depression of the braking pedal. .j-i'

In addition to the advantage already mentioned, the hydraulic systemprovided by the invention ensures that, even when shoe expander units 10provided with pistons of different cross-sectional areas are used, thevolumetric requirements of both hydraulic circuits 32 and 34 aresimilar, since both have to supply fluid to small and large diametercylinders in the expander unit.

Iclaim:

l. A vehicle braking system for a vehicle having front and rear wheels,comprising a shoe drum brake associated with each wheel, each shoe drumbrake having a leading and trailing arcuate brakeshoe, a respective shoelining being attached to each brakeshoe, a hydraulically actuatedexpander unit between one pair of adjacent ends of each shoe, a fixedanchorage arranged between the other pair of adjacent ends, saidexpander unit including oppositely directed shoe displacing pistonshaving different cross-sectional, working areas slidably housed inseparate cylinders within said expander unit, said pistons beingconstructed and arranged to move away from each other to apply thebrakes in response to fluid pressure acting on their working areas, thepiston having the larger cross-sectional working area being arranged todisplace the trailing shoe and each cylinder being inclined to assist inpositioning the center of pressure of the lining in the region of thecenter of area of said lining, said system further including a source offluid pressure, first conduit means connecting the cylinders for theleading shoes at the vehicle front wheels with the cylinders for thetrailing shoes at the vehicle rear wheels, second conduit meansconnecting the cylinders for the trailing trailing shoes at the frontwheels with the leading shoes at the rear wheels.

2. A vehicle braking system according to claim 1, wherein said first andsecond fluid pressure applying means comprises a hydraulic mastercylinder connected to each of said first and second fluid conduit means.

1. A vehicle braking system for a vehicle having front and rear wheels,comprising a shoe drum brake associated with each wheel, each shoe drumbrake having a leading and trailing arcuate brakeshoe, a respective shoelining being attached to each brakeshoe, a hydraulically actuatedexpander unit between one pair of adjacent ends of each shoe, a fixedanchorage arranged between the other pair of adjacent ends, saidexpander unit including oppositely directed shoe displacing pistonshaving different cross-sectional working areas slidably housed inseparate cylinders within said expander unit, said pistons beingconstructed and arranged to move away from each other to apply thebrakes in response to fluid pressure acting on their working areas, thepiston having the larger cross-sectional working area being arranged todisplace the trailing shoe and each cylinder being inclined to assist inpositioning the center of pressure of the lining in the region of thecenter of area of said lining, said system further including a source offluid pressure, first conduit means connecting the cylinders for theleading shoes at the vehicle front wheels with the cylinders for thetrailing shoes at the vehicle rear wheels, second conduit meansconnecting the cylinders for the trailing shoes at the front wheels withthe cylinders for the leading shoes at the rear wheels, means forapplying fluid pressure from said source to said first conduit means toactuate the leading shoes at the front wheels with the trailing shoes atthe rear wheels, and means independent of said first means for applyingsimultaneously with the said first means fluid pressure from said sourceto said second conduit means to actuate the trailing shoes at the frontwheels with the leading shoes at the rear wheels.
 2. A vehicle brakingsystem according to claim 1, wherein said first and second fluidpressure applying means comprises a hydraulic master cylinder connectedto each of said first and second fluid conduit means.